From:
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To:
Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
Cc:
Jeroen Vermeulen <jtv(at)xs4all(dot)nl>, Alex Hunsaker <badalex(at)gmail(dot)com>,
Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <gsstark(at)mit(dot)edu>,
Bart Samwel <bart(at)samwel(dot)tk>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>,
pgsql-hackers(at)postgresql(dot)org
Subject:
Re: Avoiding bad prepared-statement plans.
Date:
2010-02-26 16:27:11
Message-ID:
28767.1267201631@sss.pgh.pa.us (view raw or flat )
Thread:
2010-02-09 12:08:54 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-09 12:59:15 from Yeb Havinga <yebhavinga(at)gmail(dot)com>
2010-02-09 13:46:55 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-09 14:53:17 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-10 00:47:18 from Kris Jurka <books(at)ejurka(dot)com>
2010-02-11 03:12:41 from Bruce Momjian <bruce(at)momjian(dot)us>
2010-02-11 04:07:57 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-09 22:21:43 from Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
2010-02-09 13:50:32 from Richard Huxton <dev(at)archonet(dot)com>
2010-02-09 14:25:19 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-09 14:45:57 from Richard Huxton <dev(at)archonet(dot)com>
2010-02-09 14:10:22 from Andres Freund <andres(at)anarazel(dot)de>
2010-02-09 14:28:01 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-09 16:43:52 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-09 16:59:41 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-11 03:15:01 from Bruce Momjian <bruce(at)momjian(dot)us>
2010-02-11 06:26:15 from Дмитрий Фефелов <fozzy(at)ac-sw(dot)com>
2010-02-11 12:09:33 from Bart Samwel <bart(at)samwel(dot)tk>
2010-02-11 12:25:28 from Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
2010-02-11 12:39:49 from Bart Samwel <bart(at)samwel(dot)tk>
2010-02-11 12:41:12 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-11 12:48:14 from Bart Samwel <bart(at)samwel(dot)tk>
2010-02-11 13:04:46 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-11 16:17:40 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-11 16:39:11 from Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
2010-02-15 19:11:34 from Bruce Momjian <bruce(at)momjian(dot)us>
2010-02-15 20:03:21 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-15 20:05:29 from Bruce Momjian <bruce(at)momjian(dot)us>
2010-02-16 14:28:57 from Greg Stark <gsstark(at)mit(dot)edu>
2010-02-16 14:31:44 from Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
2010-02-16 20:17:32 from Bruce Momjian <bruce(at)momjian(dot)us>
2010-02-17 03:12:50 from Greg Stark <gsstark(at)mit(dot)edu>
2010-02-15 19:51:26 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-16 14:22:00 from Greg Stark <gsstark(at)mit(dot)edu>
2010-02-17 22:52:14 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-21 12:37:50 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-26 02:48:05 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-26 03:19:21 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-26 03:40:35 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 04:01:14 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-26 04:25:46 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-28 14:12:32 from Greg Stark <gsstark(at)mit(dot)edu>
2010-02-26 04:28:14 from Alex Hunsaker <badalex(at)gmail(dot)com>
2010-02-26 04:46:20 from Alex Hunsaker <badalex(at)gmail(dot)com>
2010-02-26 05:11:56 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 06:29:41 from Alex Hunsaker <badalex(at)gmail(dot)com>
2010-02-26 15:07:00 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 15:27:30 from Alex Hunsaker <badalex(at)gmail(dot)com>
2010-02-26 16:51:53 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-26 18:11:44 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 16:50:37 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-26 20:02:40 from Alex Hunsaker <badalex(at)gmail(dot)com>
2010-02-26 08:13:31 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-26 10:20:17 from Jeroen Vermeulen <jtv(at)xs4all(dot)nl>
2010-02-26 14:49:35 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-26 16:27:11 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 16:54:10 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-26 17:01:59 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 20:11:16 from Yeb Havinga <yebhavinga(at)gmail(dot)com>
2010-02-26 20:29:11 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-26 20:46:27 from Yeb Havinga <yebhavinga(at)gmail(dot)com>
2010-02-26 22:40:06 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-27 00:03:06 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-27 00:50:11 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-28 01:01:43 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-28 04:22:00 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-03-01 02:47:38 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-26 18:53:38 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-26 18:59:22 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 19:22:37 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-26 19:57:56 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 20:26:05 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-02-26 20:47:55 from Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
2010-02-26 19:23:22 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-03-01 11:18:01 from Yeb Havinga <yebhavinga(at)gmail(dot)com>
2010-02-28 04:20:38 from Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>
2010-02-28 07:52:55 from Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
2010-03-01 02:51:14 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-03-02 23:54:28 from Bruce Momjian <bruce(at)momjian(dot)us>
2010-03-03 05:13:46 from Robert Haas <robertmhaas(at)gmail(dot)com>
2010-02-28 08:18:26 from Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
2010-03-02 23:53:56 from Bruce Momjian <bruce(at)momjian(dot)us>
2010-02-18 14:58:25 from "Pierre C" <lists(at)peufeu(dot)com>
2010-02-18 15:09:42 from Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
2010-02-18 16:47:01 from "Pierre C" <lists(at)peufeu(dot)com>
2010-02-18 16:54:31 from Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
2010-02-18 20:19:21 from "Pierre C" <lists(at)peufeu(dot)com>
2010-02-19 02:31:05 from David Christensen <david(at)endpoint(dot)com>
2010-02-19 13:57:51 from Kenneth Marshall <ktm(at)rice(dot)edu>
2010-02-19 17:56:12 from Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
2010-02-11 13:41:02 from Yeb Havinga <yebhavinga(at)gmail(dot)com>
Lists:
pgsql-hackers
Mark Mielke <mark(at)mark(dot)mielke(dot)cc> writes:
> Will "guessing" at when the user can afford to wait longer improve the
> situation? Maybe or often, but not always.
There is no way to eliminate "guessing". The entire point here is that
we don't know whether generating a custom plan will provide a win over
not doing so, until after we've done it (and already taken the planning
time hit). We could possibly put in heuristic tests based on the
query's use of certain features; but that's still guessing, and would
take nonzero time in itself.
I concur with Jeroen's feeling that going for a simple approach first
is the way to attack this. We could design and build something vastly
more complex, then find out that it doesn't actually work much better.
Also, I think there is a lot of confusion here over two different
issues: generic plan versus parameter-specific plan, and bad planner
estimates leading to a wrong plan choice. While the latter is certainly
an issue sometimes, there is no reason to believe that it affects
prepared statements worse than non-prepared ones. So I think that
designing a fix for prepared statements on the assumption that you can't
trust the planner's estimates is solving the wrong problem.
regards, tom lane
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